One of the main problems with electrophotographic copiers arises from the desire for speed in copy production. After a photoconductor has been charged, the energy required to produce a latent image in light and shade of the original of sufficient contrast to produce an acceptable copy is a function of the quantum of light falling upon the photoconductor and the light sensitivity of the photoconductor. Ideally, the illumination of the photoconductor should be such that the brightest part of the image will be fully discharged while the darkest part of the image will leave the photoconductor fully charged. In practice, this is never achieved, owing to the limits of the light response of known photoconductors. In the current state of the art of photocopying machines, when the speed of producing copies exceeds about 30 copies per minute, the energy required to operate the copier approaches 1500 watts. Since the ordinary potential in office and house wiring is 110 volts, the power from a given outlet is limited to 1500 watts. Accordingly, to product satisfactory copies at a higher rate, a special electrical installation will be required. This means that the copying machine cannot be decentralized, but must be located in the region of the higher voltage outlet. Furthermore, the high energy will produce thermal problems, both in respect of the photoconductor and in the environment, aside from the expense of energy consumption. Because of these problems, many efforts are being made to increase the light sensitivity of photoconductors.